A fuel cell system includes a fuel cell that generates electricity through an electrochemical reaction between a fuel gas and an oxidizing gas (reaction gases), a gas-supplying flow path that supplies the reaction gases to the fuel cell, and a gas-discharging flow path that discharges the reaction gases from the fuel cell. Open/close valves for the fuel cell, corresponding to the fluid control valve, can be provided in the gas-supplying flow path and the gas-discharging flow path.
For example, an open/close valve for a fuel cell disclosed in JP 2004-183713 A includes a valve member having a pillar portion, which is movable in its axial direction to close or open the gas flow paths. The open/close valve for a fuel cell includes a diaphragm that divides an internal space into two chambers. The open/close valve is provided at a hydrogen-discharging portion that discharges hydrogen exhausted from the fuel cell. A path branched from an air-supplying path, which supplies air to the fuel cell, is connected to one chamber of the two chambers of the open/close valve. A coil spring is provided in the other chamber of the two chambers. The coil spring resiliently urges the valve member so as to open the other chamber and discharge the discharged hydrogen. If air is supplied to one chamber of the valve in an operating state, fluid pressure acts on the diaphragm to cause the valve member to contact a valve seat against an elastic force of the coil spring while the other chamber is closed.
A fuel cell system disclosed in JP 2004-185831 A includes a pressure control unit provided in a gas-supplying flow path that supplies an anode side fuel gas to a fuel cell stack, and a shutoff valve provided on a gas upstream side of the pressure control unit. The shutoff valve includes a valve member connected to a plunger, which departs from a valve seat to open the valve when its solenoid is excited. The valve member is tilted relative to the up-and-down direction on the drawing surface (refer to FIG. 7 illustrated in JP 2004-185831 A).
A fuel cell system disclosed in JP 2006-32134 A includes a gas discharge tube connected to a vapor-liquid separator that separates gas and fluid from an anode side fuel gas. A discharge valve provided in the gas discharge tube includes a valve seat and a valve member tilted relative to the gravity-acting direction at an angle greater than 0 and less than 90 degrees (e.g., 45 degrees) in a direction opposed to the discharge direction of the anode discharge gas.
A drain apparatus for a fuel cell system disclosed in JP 2004-311222 A includes an open/close valve attached to an inclined surface formed at a lower portion of a water reservoir tank. The open/close valve opens and closes in response to a valve-opening signal or a valve-closing signal.
According to the open/close valve for a fuel cell disclosed in JP 2004-183713 A, the valve member and the valve seat are not tilted relative to the gravity-acting direction. Therefore, during or stopping an operation of the fuel cell, water or liquefied water vapor, if contained in the gas flowing in the flow path, may remain at a peripheral portion of the valve seat where the valve seat contacts the valve member. If the remaining water freezes at or below the freezing point, the open/close valve may fail to open and close smoothly.
For example, in a fuel cell system, gas flowing in a gas flow path may contain water or water vapor for either of the following two reasons. As one reason, if a humidifier is provided in a gas-supplying flow path to increase the power generation efficiency of the fuel cell, water vapor contained in the gas may liquefy on a humidifier downstream side when the humidifier humidifies the gas. As another reason why the gas flowing in the gas flow path may contain water or water vapor, water is a by-product of the power generation by the fuel cell and the water may be contained in the gas discharged from the fuel cell. If the gas contains water or water vapor as described above, water may remain in the periphery of pressing surfaces, which press against each other, of the valve member and the valve seat. If the water freezes, the open/close valve may fail to open and close smoothly.
Meanwhile, according to the discharge valve provided in the fuel cell system disclosed in JP 2006-32134 A, a surface of the valve seat to be pressed against the valve member is tilted relative to the gravity acting direction, i.e., the vertical direction. However, the pressing surface of the valve seat to be pressed against the valve member is positioned low on an upstream side of gas flowing in a flow path and high on the gas downstream side. When the pressing surface of the valve seat is tilted, the flow of gas in operation may cause water to flow upward along the pressing surface. In other words, the flow of gas may prevent the water from falling due to gravity along the down slope of the pressing surface. In short, the effect of gravity that causes the water to fall along the pressing surface may be cancelled by the effect of flowing gas that causes the water to move upward along the pressing surface. Therefore, when the fuel cell system is in operation, the tilted configuration of the valve seat may fail to be effectively used to remove the water from the pressing surface of the valve seat and may not be able to prevent freezing of the remaining water. Thus, the valve may fail to open and close smoothly in a low-temperature environment.
According to the shut off valve of the fuel cell system disclosed in JP 2004-185831 A, although the valve member and the valve seat are tilted relative to the up-and-down direction on the drawing surface, the shutoff valve includes no configuration tilted relative to the gravity-acting direction. Even if the up-and-down direction relative to which the valve member and the valve seat are tilted is the gravity-acting direction, the pressing surface of the valve seat to be pressed against the valve member is set low at the upstream side of the gas flowing in the flow path and high at the gas downstream side. Therefore, the shutoff valve may need to overcome inconvenience similar to that of the discharge valve disclosed in JP 2006-32134 A.
According to the open/close valve attached to the inclined surface formed at the lower portion of the water reservoir tank disclosed in JP 2004-311222 A, the open/close valve is not employed to close or open the gas flow path in which gas flows and is therefore unable to function as a fluid control valve that closes or opens the gas flow path according to a displacement in an axial direction of a valve member having a drive shaft.
An object of the present invention is to make it to effectively perform, in a fuel cell system, smooth opening and closing of a fluid control valve for its operation even in a low-temperature environment.